fix #27532, implementing a native type with fields

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This library defines the operations that define and manipulate Dart
 /// classes.  Included in this are:
 ///   - Generics
 ///   - Class metadata
 ///   - Extension methods
 ///
@@ skipping 441 matching lines @@
 // TODO(jmesserly): essentially this gives two names to the same method.
 // This benefit is roughly equivalent call performance either way, but the
 // cost is we need to call defineExtensionMembers any time a subclass
 // overrides one of these methods.
 defineExtensionMembers(type, methodNames) => JS(
     '',
     '''(() => {
   let proto = $type.prototype;
   for (let name of $methodNames) {
     let method = $getOwnPropertyDescriptor(proto, name);
-    // TODO(vsm): We should be able to generate code to avoid this case.
-    // The method may be null if this type implements a potentially native
-    // interface but isn't native itself.  For a field on this type, we're not
-    // generating a corresponding getter/setter method - it's just a field.
-    if (!method) continue;
     $defineProperty(proto, $getExtensionSymbol(name), method);
   }
   // Ensure the signature is available too.
   // TODO(jmesserly): not sure if we can do this in a cleaner way. Essentially
   // we need to copy the signature (and in the future, other data like
   // annotations) any time we copy a method as part of our metaprogramming.
   // It might be more friendly to JS metaprogramming if we include this info
   // on the function.
   let originalSigFn = $getOwnPropertyDescriptor($type, $_methodSig).get;
   $defineMemoizedGetter(type, $_methodSig, function() {
@@ skipping 61 matching lines @@
 ///
 /// The constructor
 defineNamedConstructorCallable(clazz, name, ctor) => JS(
     '',
     '''(() => {
   ctor.prototype = $clazz.prototype;
   // Use defineProperty so we don't hit a property defined on Function,
   // like `caller` and `arguments`.
   $defineProperty($clazz, $name, { value: ctor, configurable: true });
 })()''');